Lunchbox locker acting a little unruly Dana 35

[Skierman]

Ok, so I am trying to understand what I was feeling with a lunchbox locker (installed by a previous owner) in the rear of my 1999 TJ. Accelerating or decelerating felt like the jeep was rear steering just a little occasionally. I had been into the rear diff previously and I would say that the clearances between the halves of the locker were a little excessive, and I think the locker under normal light loaded conditions was engaging only one axle shaft. Add a little more load and it would hook up the rest of the axle, but it was acting like it took a lot to get there. Additionally, lifting a tire in the air and spinning it by hand, it would free spin (no locking, no clicking) as if it was just not engaging the teeth of the locker at all.

I have since removed the locker and replaced it with new spider gears and it tracks straight and true now as an open diff. The old cross pin in the locker was worn and was resulting in a lot of drivetrain slop and clunking-this is now totally remedied. Has anyone else seen this, or have some guidance on how an auto locker (properly installed) should feel?

 

[CharlesHS]

Depending upon how old the lunch box locker is... several years ago a couple of the manufacturers notified retailers that the cross pin metals had been reformulated. Powertrax was one that comes to mind and there were a couple others.

 

[Jerry Bransford]

Ok, so I am trying to understand what I was feeling with a lunchbox locker (installed by a previous owner) in the rear of my 1999 TJ. Accelerating or decelerating felt like the jeep was rear steering just a little occasionally. I had been into the rear diff previously and I would say that the clearances between the halves of the locker were a little excessive, and I think the locker under normal light loaded conditions was engaging only one axle shaft. Add a little more load and it would hook up the rest of the axle, but it was acting like it took a lot to get there. Additionally, lifting a tire in the air and spinning it by hand, it would free spin (no locking, no clicking) as if it was just not engaging the teeth of the locker at all.

I have since removed the locker and replaced it with new spider gears and it tracks straight and true now as an open diff. The old cross pin in the locker was worn and was resulting in a lot of drivetrain slop and clunking-this is now totally remedied. Has anyone else seen this, or have some guidance on how an auto locker (properly installed) should feel?

Generally speaking a lunchbox locker in a rear axle will be very poorly behaved, while the exact same brand of locker will be very well behaved when installed into the front axle. The reason a rear-mounted lunchbox locker is poorly behaved is because that axle constantly receives torque from the engine whether you're in 2wd or 4x4 which makes it hard for the locker to unlock around corners.

My caution though is that the stock Dana 35 axle shafts are not strong enough for any kind of locker. At some point you can expect a snapped axle shaft because a locker can double the load seen by one side's axle shaft.

This is what happened to a friend of mine's Dana 35 with a locker, I was right behind her and heard it snap when it happened. It took us a while to get her back to camp so we could swap out that broken axle shaft. She was only smiling after we were nearly done and she knew she could drive home the next day.

 

[Skierman]

Generally speaking a lunchbox locker in a rear axle will be very poorly behaved, while the exact same brand of locker will be very well behaved when installed into the front axle. The reason a rear-mounted lunchbox locker is poorly behaved is because that axle constantly receives torque from the engine whether you're in 2wd or 4x4 which makes it hard for the locker to unlock around corners.

My caution though is that the stock Dana 35 axle shafts are not strong enough for any kind of locker. At some point you can expect a snapped axle shaft because a locker can double the load seen by one side's axle shaft.

This is what happened to a friend of mine's Dana 35 with a locker, I was right behind her and heard it snap when it happened. It took us a while to get her back to camp so we could swap out that broken axle shaft. She was only smiling after we were nearly done and she knew she could drive home the next day.

View attachment 176072

Yeah, I knew that I did not want a locker in this axle just on general principle. I did put the open diff back in.
When I do get a better axle under this Jeep, is it necessary to do control arms as well in order to avoid torque steer or was that likely a problem resulting from this poor set up?
Thanks for your help

 

[Jerry Bransford]

Yeah, I knew that I did not want a locker in this axle just on general principle. I did put the open diff back in.
When I do get a better axle under this Jeep, is it necessary to do control arms as well in order to avoid torque steer or was that likely a problem resulting from this poor set up?
Thanks for your help

Whether you need different control arms has to do with your suspension lift height, whether or not the rear driveshaft is replaced with a double-cardan design, and the level of trail difficulty you plan to do. At stock or near stock suspension heights the factory control arms work well. It's once you get to tall lift heights and/or installing a double-cardan rear driveshaft when new control arms are going to be needed.

 

[Skierman]

Whether you need different control arms has to do with your suspension lift height, whether or not the rear driveshaft is replaced with a double-cardan design, and the level of trail difficulty you plan to do. At stock or near stock suspension heights the factory control arms work well. It's once you get to tall lift heights and/or installing a double-cardan rear driveshaft when new control arms are going to be needed.

Got it. Thank you.